Generally, solar cars convert light energy into electric energy through solar cells, provided at fixed locations on a vehicle, to charge batteries, the energy from which is used to drive and vehicle.
However, as the amount of electric energy converted in the solar cells and the amount of electric energy able to be discharged by the batteries is limited, a control system is needed to maximize the use of energy.
In the prior art solar car, when cruise control is selected by the driver, energy usage is optimized by utilizing either a speed cruise control method in which vehicle speed is maintained at a constant level, or an electric power cruise control method in which a predetermined amount of electric power is consumed at a constant level.
In the above speed cruise control method, a control line is achieved only on the basis of a pre-set vehicle speed. Accordingly, if there are changes in road gradient, the amount of wind or other factors that affect drive resistance, energy consumption levels are varied to maintain the vehicle at a constant speed.
So, for example, when driving in a state of 0% drive resistance (i.e., a level road surface and no wind or other factors affecting drive resistance being present) with the cruise speed set at 81 km/h such that electric energy consumption is 1200W, if one of the factors changes to increase drive resistance, a central processing unit (CPU) outputs a signal to increase torque to maintain the 81 km/h cruise speed. Accordingly, the amount of energy consumed increases such that energy efficiency decreases.
Further, in this high-torque and low-efficiency operational state, motor efficiency is worsened by an increase in temperature, and capacity, energy efficiency, and life of the batteries are reduced.
If the electric power cruise control method is used, a control is achieved only on the basis of a pre-set level of energy consumption. Accordingly, if changes occur in drive resistance, because the CPU performs control to consume a predetermined amount of electric power at a constant level, vehicle speed is not uniformly maintained such that the advantages of cruise control are negated.
This overloads the motor and reduces the life of the same as drive efficiency is negatively influenced.